Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 270727
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
327 AM EDT Thu Apr 27 2017

LATEST UPDATE...
Synopsis/Short Term/Long Term/Marine

.SYNOPSIS...
Issued at 328 AM EDT Thu Apr 27 2017

A storm system tracking northward across Lake Michigan today will
push a cold front through the area this morning. Expect a period
of showers and even an isolated thunderstorm with the passage of
that cold front. This is a strong cold front so once it is through
we will see temperatures falling during the afternoon with gusty
winds.

&&

.SHORT TERM...(Today through Saturday)
Issued at 328 AM EDT Thu Apr 27 2017

Today we have strong surface low with good upper air support
lifting northward through Lake Michigan this morning reaching Lake
Superior by this afternoon. This sweeps a strong cold front
through the area this morning. There is an area of heavy rain and
isolated thunderstorms near the surface low. That area of rain
should track nearly due north across areas west of US-131 during
the mid morning hours. The question of the day through is will
there be a line of convection with the cold front as is sweeps
east across our area mid to late morning? At this point it seems
questionable and it would be more likely for that line to form
over SE Lower Michigan by early this afternoon.

Once all that is done we are in the cold air in the wrap around
the departing deep surface low so it will be windy with
temperatures falling into the upper 40s to mid 50s by late in the
day today. A weak surface ridge builds in Friday morning so winds
will let up and skies may be partly cloudy.

There seems to be an overrunning event Friday afternoon into
Friday evening This is one of those jet entrance region lift sort
of events. Seems with this one the QPF will be light as there is
not a lot of mid level moisture for this system.

The main system come out into our area later Saturday into Sunday.
This event we have been writing about for over a week now. Between
the departing showers late Friday night and the income rain later
Saturday, expect another quiet weather periods.



.LONG TERM...(Saturday night through Wednesday)
Issued at 328 AM EDT Thu Apr 27 2017

An active weather pattern will continue to develop Saturday night
through Monday as abundant gulf moisture will move northward into
the lower Great Lakes region along with strong 1000-850 mb moisture
transport. Precipitable water values will rise to 1.5 to 1.75 inches
by Sunday.

As such medium range guidance trends remain quite consistent in
showing potential for widespread rain over our fcst area Saturday
night through Sunday night that will likely be heavy at times. The
evolution of the synoptic pattern is conducive to a widespread 1 to
3 inch type rainfall over our fcst area Saturday night through
Monday afternoon with locally higher amounts.

Some convection is possible as well in this time frame although a
consensus of latest medium range guidance suggests that stronger
instability conducive to more robust convective development will
stay well south of our fcst area. So overall at this time fcst
concerns involve heavy rain and potential hydrological issues more
so than severe convective concerns.

A cooler airmass will advect in on the back side of the system
beginning late Monday with lingering showers. Cooler and unsettled
weather with more showers will continue Tuesday before more tranquil
wx returns by midweek

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1159 PM EDT Wed Apr 26 2017

A mix of vfr/mvfr conditions should gradually deteriorate to
mainly mvfr overnight due to low clouds and scattered rain
showers. Isolated thunderstorms may also affect mainly the KAZO
and KGRR terminals during the next couple of hours.  Conditions
will then remain mainly mvfr Thursday morning and early afternoon
due to low clouds and scattered showers.

A line of showers and perhaps isolated thunderstorms will move
through early Thursday afternoon right along the cold front. Conditions
will then improve to vfr mid to late Thursday afternoon after the
frontal passage.

South to southwest winds will increase to around 15 to 20 kts by
late Thursday morning prior to frontal passage and will veer to
the west and increase to around 15 to 20 kts with gusts to near 25
kts after fropa. Conditions will then remain vfr through Thursday
evening.

&&

.MARINE...
Issued at 328 AM EDT Thu Apr 27 2017

I will keep the SCA going as is. Winds will let up tonight, at
least some.

&&

.HYDROLOGY...
Issued at 325 PM EDT Wed Apr 26 2017

Confidence continues to grow that we will have an increasing flood
risk as we head into the weekend and next week. The GFS, GEM, and
ECMWF all have been indicating a pattern that will produce
significant rainfall for our region, likely on the order of 2" to 3"
or more. When that much rain falls across the entire reaches of the
major basins - Grand, Muskegon, and Kalamazoo - there will be some
significant rises. Trends will continue to be monitored.

Smaller rivers and streams are going to be highly responsive to this
type of rain, with abrupt rises possible. Residents along smaller
rivers and streams should be aware of the risk for these types of
changes late into the weekend and early next week.

At this point it is too early to tell exactly how high the rivers
will get, but flood stage may be exceeded at many locations
potentially.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 2 AM EDT Friday for LMZ844>849.

&&

$$

SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...Laurens
AVIATION...Laurens
HYDROLOGY...Hoving
MARINE...WDM



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